Amebic Liver Abscess

Essentials of Diagnosis

• Fever, abdominal pain

• Amoebae or antigen in stool or abscess aspirate

• Positive serologic tests but may represent prior infections

• Hepatomegaly, hepatic abscess on imaging studies

General Considerations

• The Entamoeba complex contains three morphologically identical species

  • E dispar, which is avirulent

  • E moshkovskii, which is also avirulent

  • E histolytica, which may be an avirulent intestinal commensal or lead to serious disease

• Humans are the only established host for E histolytica

• Transmission occurs through ingestion of cysts from fecally contaminated food or water

• Infection can be transmitted person-to-person

• Flies and other arthropods also serve as mechanical vectors

• Disease follows penetration of the intestinal wall, resulting in

  • Diarrhea

  • Dysentery

  • Extraintestinal disease, most commonly liver abscess

Demographics

• E histolytica infections are present worldwide but are most prevalent in subtropical and tropical areas under conditions of crowding, poor sanitation, and poor nutrition

• Of 500 million persons worldwide infected with Entamoeba, most are infected with E dispar and an estimated 10% (50 million) are infected with E histolytica

• Mortality from invasive E histolytica is about 100,000 per year

• Severe disease is more common in

  • Young children

  • Pregnant women

  • Persons who are malnourished

  • Persons receiving corticosteroids

• Hepatic abscesses more common in men

Symptoms and Signs

• Many patients do not have current or a past history of intestinal symptoms

• Acute or gradual onset of abdominal pain

• Fever

• Enlarged and tender liver

• Anorexia

• Weight loss

• Intercostal tenderness

• Diarrhea is present in a small number of patients

• Abscesses are most commonly single and in the right lobe of the liver

• Amebic infections may rarely occur throughout the body, including the lungs, brain, and genitourinary system

Differential Diagnosis

• Pyogenic liver abscess

• Echinococcosis (hydatid disease)

• Cholecystitis or cholangitis

• Right lower lobe pneumonia

• Pancreatitis

• Hepatocellular carcinoma

Laboratory Tests

• Leukocytosis and elevated liver biochemical tests

• Serologic tests for anti-amebic antibodies are almost always positive, except very early in the infection

• Thus, a negative test in a suspicious case should be repeated in about a week

• The stool E histolytica antigen test is positive in ~40% of cases; the TechLab II test can also be used to test serum, with good sensitivity if used before the initiation of therapy

• Examination of stools for the organisms or antigen is frequently negative

Imaging Studies

• Ultrasonography, CT, or MRI show abscesses as round or oval low-density nonhomogeneous lesions with abrupt transition from normal liver to the lesion and hypoechoic centers

Diagnostic Procedures

• Percutaneous aspiration

  • May be needed to distinguish between amebic and pyogenic abscesses

  • Best done by an image-guided needle

  • Typically yields brown or yellow fluid

  • Detection of organisms in the aspirate is uncommon, but detection of E histolytica antigen is very sensitive and diagnostic

  • The key risk is peritoneal spillage leading to peritonitis from amoebae or other (pyogenic or echinococcal) organisms

Medications

• See Table 35–6

• Treatment is tinidazole or metronidazole plus a luminal agent

• Intravenous metronidazole can be used when necessary

• If initial treatment with metronidazole or tinidazole fails, add chloroquine, emetine, or dehydroemetine

• Neither emetine nor dehydroemetine are available in the United States

Therapeutic Procedures

• Needle aspiration may be helpful for large abscesses (over 5–10 cm), in particular if

  • The diagnosis remains uncertain

  • There is an initial lack of response

  • Patient is very ill, suggesting imminent abscess rupture

Complications

• Without prompt treatment, amebic abscesses may rupture into the pleural, peritoneal, or pericardial space, which is often fatal

Prognosis

• With successful therapy, abscesses disappear slowly (over months)

Prevention

• Safe water supplies; water can be

  • Boiled

  • Treated with iodine (0.5 mL tincture of iodine per liter for 20 min; cysts are resistant to standard concentration of chlorine)

  • Filtered

• Sanitary disposal of human feces

• Adequate cooking of foods

• Protection of foods from fly contamination

• Handwashing

• In endemic areas, avoidance of foods that cannot be cooked or peeled

When to Admit

• All patients should be admitted